What is Variable Resistor (Preset)?

This type of variable resistor (a preset) is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than normal variable resistors so they are often used in projects to reduce the cost.

Radio Frequency Test Station | Electronics Books & Tutorials

Instruments guides, Books, tutorials and techniques for Technicians and Engineers on Designing Circuits and Test Stations use for Electronics Testing and Measurements